I gotta say, whilst I appreciated its purpose (and the purpose of most Asylum flicks), I really disliked Sharknado. My main point of comparison is Mega Shark vs. Giant Octopus. With MSvGO there was a massive sense of spectacle. It god awfully stupid but there was some special level of spectacle, when the Mega Shark first appeared, when the Giant Octopus first appeared, the destruction they wrought, etc etc all leading to the final showdown. With Sharknado, I didn't feel that. There was too much time spent lingering on the main character and the family dispute/character building, which was a lot to its detriment since it's obvious the film didn't care about that kinda stuff. It wasn't really until the final 10-15 minutes that the spectacle really started to kick in. Comparatively with MSvOG it felt a lot like a spectacle throughout to me.
But then again, it's worth noting that for me, MSvOG was the "first" of its kind (its kind being Asylum's cheap, purposely bad Syfy releases) which bestowed upon it a kind of special "Wow, I've not watched something like this before - it's like special levels of stupid and special levels of awesome all in one." By the time Sharknado had rolled around, and I'd sat through a few of these Syfy Mockbusters, that novelty had worn off for me.